She usually leaves her house before 11 o’clock so I deduce that she has definitely left the house.'She must have left the house by now it’s nearly 11 o'clock.'.
We use 'must have', 'can't have' and 'might have' in the same way as the present perfect - the action we are describing happened, or did not happen, in the past and is still true in the present. We use the modal verbs 'must have', 'can't have' and 'might have' to make guesses or deductions about an action in the past that we believe has definitely happened, has definitely not happened or possibly happened, based on our knowledge, information or evidence, or lack of it.
